Histochemical and mechanical properties of diaphragm muscle in morbidly obese Zucker rats

Abstract

The purpose of the present study was to evaluate the effects of chronic mass loading produced by obesity on the structural and functional characteristics of the diaphragm in lean and obese Zucker rats. The trapezius muscle served as an internal control. The studies were carried out on 17 lean (303 +/- 24 g) and 16 obese (698 +/- 79 g) Zucker rats. We observed that the diaphragms from obese animals were restructured such that the overall contribution of type I and IIa fibers was significantly increased. As a consequence of this remodeling, overall diaphragm thickness was selectively greater in obese animals. In small isolated diaphragm bundles studied in vitro, we also detected a reduction in specific force in obese animals that was not detected in the trapezius muscle. In vitro fatigue resistance, assessed by repeated stimulation, was similar in muscles of lean and obese animals. Diaphragm fiber oxidative capacity (succinate dehydrogenase activity) was also comparable in lean and obese animals. We conclude that in obesity the diaphragm undergoes modest remodeling that may be beneficial in enhancing force generation.

Physiologic correlates of dyspnea in patients with morbid obesity

“…There are no available data on diaphragm morphology and histochemistry in human obesity. In obese rats, a fast to slow shift in myosin heavy-chain isoforms of diaphragm and parasternal fibers has been described, 32 which would rather favor an enhanced resistance to fatigue of these muscles. This adaptive shift in MHC isoforms to inspiratory load is prevented by early leptin administration in young ob mice.…”

Noninvasive assessment of the tension–time index of inspiratory muscles at rest in obese male subjects

“…25 A severe decline in inspiratory muscle strength can lead to impaired airway clearance and inadequate ventilation. 26 Farkas et al 27 have demonstrated that in the Zucker 'fatty' rat (the most frequently studied animal model of obesity), the overall proportion of oxidative fibers (types I and IIa) increases, as do diaphragm thickness and mass. Despite these changes, the diaphragm's mean force-generating capacity (indexed to its cross-sectional area) is 15% lower than in lean litter mates.…”

Pulmonary Function Tests, Respiratory Muscle Strength, and Endurance of Persons With Obesity

“…The energy consumption increases fourfold in subjects suffering from obesity and sevenfold in OHS compared with normal subjects [6]. The various effects of obesity on pulmonary muscles have been studied in previous reports [4,7,8]. This study was planned …”